Glaucopsyche lygdamus
Silvery Blue

Family Description:
Note: This species consists of approximately ten races or subspecies, all of which vary slightly in appearance.

The caterpillar varies in color, ranging from gray to green to brown, and is covered with white hair. It may be marked with a dark green or red stripe running lengthwise along the back and light diagonal dashes on the side. Its average, full-grown length is 3/4 inch.
Adult: This is a fairly small butterfly, with a wingspan of 7/8 to 1 1/4 inches. The male is silvery blue on the upperside, with the wings edged in black. The female is blue to brown on the upperside, and the wings are edged with a thicker black border. Both the male and the female may have a purplish cast. Underneath, both sexes are gray to brown and marked with an uneven row of white-edged black dots.

This widespread species ranges from Alaska through most of Canada to Nova Scotia; through the western third of the U.S.; through the northern U.S. and a portion of the southeastern U.S. It occurs through most of Idaho.


It can be found in a variety of habitats, including meadows, fields, open woodlands, coastal dunes, and along streams.


Caterpillar: Caterpillars feed on new leaves, flowers, and fruits of legumes, such as milk vetches (Astragalus spp.), other vetches (Vicia spp.), peas (Lathyrus spp.), lupines (Lupinus spp.), and deer weed (Lotus scoparius).
Butterflies drink flower nectar

The caterpillar is equipped with a honey gland, also known as a dorsal nectary organ, which emits a sugary solution agreeable to ants. The ants feed on the solution and in turn protect the caterpillar from predators. Also for protection, the caterpillar bears a pair of everscible tubercles or tentacles on the eighth segment. These tubercles are usually housed within the body, but when the caterpillar feels threatened by the approach of a potential predator, they can be pushed out to release a chemical which mimics an ant alarm pheromone. This scent causes the ants to become frenzied and aggressive, and the potential predator takes leave or is eaten by the ants. There is only one new generation of caterpillars each growing season. Each caterpillar undergoes four stages of growth, called instars. Pupae overwinter in a physiological state called diapause. Adults generally fly from April to June, but may be seen as early as February and as late as August in some locations. The butterflies are one of the first species typically seen in the spring.


Males actively patrol in search of receptive females. Females lay eggs singly on the flower buds or new leaves of host plants.

Idaho Status: Unprotected nongame species.
Global Rank: G5; most populations are widespread, abundant, and secure. One subspecies in California, once thought to be extinct, is ranked T1, which means it is critically imperiled because of extreme rarity and is imminently vulnerable to extinction.

Ballmer, G. R. and G. F. Pratt. 1988. A survey of the last instar larvae of the Lycaenidae of California. Journal of Research on the Lepidoptera 27:1-81.

Ferris, C. D. and F. M. Brown. (eds.) 1981. Butterflies of the Rocky Mountain States. Univ. of Oklahoma Press, Norman, Oklahoma, USA, 442 pp.

Opler, P. A., H. Pavulaan, and R. E. Stanford. 1995. Butterflies of North America. Jamestown, North Dakota, USA: Northern Prairie Wildlife Research Center Home Page. (Version 05Nov98).

Opler, P. A. and A. B.Wright. 1999. A Field Guide to the Western Butterflies.   Second Edition.  Peterson Field Guide Series. Houghton Mifflin Company, New York, New York, USA, 540 pp.

Pyle, R. M. 1981. National Audubon Society Field Guide to North American Butterflies. Alfred A. Knopf, Inc., New York, New York, USA, 924 pp.

Scott, J. A. 1986. The Butterflies of North America. Stanford University Press, Stanford, California, USA, 583 pp.

Stanford, R. E. and P. A. Opler. 1993. Atlas of Western U.S.A. Butterflies (Including Adjacent Parts of Canada and Mexico). Published by authors, Denver, Colorado, USA, 275 pp.